title: Evaluation of molecular mass and tacticity of polyvinyl alcohol by non-equilibrium capillary electrophoresis of equilibrium mixtures of a polymer and a dye.
abstract: Non-equilibrium capillary electrophoresis of equilibrium mixtures (NECEEM) has been used to characterize polyvinyl alcohol (PVA). Commercial PVA samples with different molecular masses, from M(w)=15 up to 205 kDa, were used. According to the (13)C NMR spectra, the samples also differed in tacticity (stereoregularity). Mixtures of PVA and the anionic azo-dye Congo Red (CR) were injected in the presence of a borate buffer. The electropherograms gave a band and a peak due to the residual PVA-CR complex and the excess dye, respectively, plus a superimposed exponential decay due to the partial dissociation of the complex during migration. The stoichiometry of the PVA-CR complex, q=[monomer]/[dye], reached a maximum, q(sat), which depended on both M(w) and tacticity of PVA. Thus, q(sat) decreased from a molar ratio of ca. 4.9 to 3.6 at increasing M(w) values, this variation also being largely dependent on tacticity. A similar dependence of the electrophoretic mobility of the complex on both M(w) and tacticity was also observed. A possible explanation, based on the formation of a stack of CR ions inside the PVA-CR complex, was proposed and discussed. Finally, at increasing M(w) values, the stability constant of the complex increased slightly, and the pseudo-first order dissociation rate of the complex decreased, this later parameter also showing a dependence on both M(w) and tacticity.
authors.affiliation: Departament de Química Analítica, Universitat de València, Dr. Moliner 50, 46100 Burjassot, Valencia, Spain.
authors.forename: Enrique Javier
authors.initials: EJ
authors.lastname: Carrasco-Correa
authors.forename: Miriam
authors.initials: M
authors.lastname: Beneito-Cambra
authors.forename: José Manuel
authors.initials: JM
authors.lastname: Herrero-Martínez
authors.forename: Guillermo
authors.initials: G
authors.lastname: Ramis-Ramos
mesh_terms: D001391:Azo Compounds / Q000737:chemistry*; D001881:Borates; D003224:Congo Red / Q000737:chemistry; D019075:Electrophoresis, Capillary / Q000379:methods*; D008970:Molecular Weight; D011142:Polyvinyl Alcohol / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet
chemical_list: D001391:Azo Compounds; D001881:Borates; D003224:Congo Red; D011142:Polyvinyl Alcohol